This study was carried out to suggest basic data of green roof system effective for further improvement of urban thermal environment by implementing quantification of improving effect of urban thermal environment and heat budget along plant material and using extensive modular green roof systems that were planted with Sedum sarmentosum and Zoysia japonica. Plant length, coverage ratio, content of chlorophyll, leaf area, fresh weight and dry weight were measured as plant growth. Temperature reduction effect was measured by installing thermocouple and heat flow meter at surface of concrete, surface of green roof and inside of soil. Heat budget analysis was performed by measuring long and short wave radiation, net radiation and evapotranspiration. The surface temperature of concrete was highest followed by the plots planted with S. sarmentosum and Z. japonica, respectively, and temperature reduction effect by green roof proved. Temperature reduction at below soil was the highest at surface of concrete and there was a small difference between S. sarmentosum and Z. japonica. It appeared that the highest point of green roof temperature was delayed about 2 hours comparing with surface of concrete. The temperature of each measuring point appeared high in order of surface of green roof, bottom of soil and inside of soil. Plant types, temperature and soil water influenced on green roof surface temperature and it appeared that green roof surface temperature was influenced on temperature of below soil. As the result of analyzing radiant balance along establishment of green roof, while downward-short wave radiation (S↓) showed similar tendency at all plots, surface of concrete showed the highest upward-short wave radiation(S↑), and S. sarmentosum and Z. japonica followed after that. Downward-long wave radiation (L↓) did not show the difference at all plots and surface of concrete showed the highest upward-long wave radiation (L↑), and S. sarmentosum and Z. japonica followed after that in sequential order. Net radiation appeared the highest when establishing green roof and albedo appeared to be lowered when establishing green roof comparing with surface of concrete. Z. japonica was greater than S. sarmentosum regarding evapotranspiration. As the regression analysis of weather conditions, the increased evapotranspiration of Z. japonica was higher than that of S. sarmentosum as temperature got higher. While such result showed the similar tendency even in comparison with relative humidity, it appeared the wind velocity did not influence on evapotranspiration. The evapotranspiration of Z. japonica became greater as its deficiency of saturation was higher, but evapotranspiration of S. sarmentosum had nothing to do with its deficiency of saturation. As the result of heat budget analysis, the production of sensible heat was high and it decreased in case of green roof. Latent heat production of Z. japonica was higher than S. sarmentosum and conduction heat within the building appeared to decrease.